1. Field of the Invention
The present invention relates to a frame for a semiconductor package in which a semiconductor device is mounted on a lead frame and the outer surface of the semiconductor device, particularly the upper surface of the semiconductor device, is encapsulated with molding compound.
2. Description of the Prior Art
In recent years, it has been necessary to miniaturize and shape semiconductor products mounted on a substrate so as to be thinner, since the packaging of the semiconductor is more dense. It has been required for Large Scale Integration (LSI) to reduce the number of chips by improving integration level and to miniaturize and make a package lighter. The popularization of so-called Chip Size Package (CSP) is rapidly advancing. Particularly, in the development of a thin semiconductor product with a lead frame, the semiconductor package of the single side encapsulation type has been developed in which a semiconductor device is mounted on a lead frame and the surface of semiconductor device mounted on a lead frame is encapsulated with molding compound.
FIG. 1 is a sectional view of one example of a semiconductor package. FIG. 2 is a plan view thereof. The semiconductor package shown in FIGS. 1 and 2 is comprised of a lead frame 1, a semiconductor device 4 mounted on a die-pad 3 supported with suspending leads 2 of lead frame 1, metallic thin wires 6 for electrically connecting electrodes provided on the top face of the semiconductor device 4 with terminals 5 of lead frame 1, and molding compound 7 for encapsulating the outer region of semiconductor device 4 including the upper side of semiconductor device 4 and the lower side of die-pad 3. The semiconductor package is of the non-lead type in which so-called outer leads do not project from the semiconductor package and the two inner leads and outer leads are integrated into terminals 5, wherein the lead frame 1 is half-cut by etching or is half-etched in such a manner that die-pad 3 is positioned higher than terminals 5. Since a step is formed between die pad 3 and terminals 5, molding compound 7 can be inserted into the lower side of die-pad 3 so that a thin semiconductor package can be realized even though the semiconductor package has a non-exposed die-pad.
Since the semiconductor device is miniature, a matrix type frame is mainly used for the above-mentioned semiconductor package of the non-lead type, in which plural semiconductor devices are arranged in a direction of a width of the matrix type frame. Further, recently, due to a demand for lower cost, a switch from a frame of the individually molded type shown in FIGS. 3A and 3B to a frame of the collectively molded type shown in FIGS. 4A and 4B is occurring.
In the frame of the individually molded type, as shown in FIG. 3(A), individual molding cavities C of a small size are provided separately within a frame F. After molding, individual semiconductor packages are stamped out so that semiconductor packages S shown in FIG. 3(B) are obtained. Namely, semiconductor devices are mounted on die-pads of lead frames through silver paste and others, and wire bonding is carried out. Thereafter, the respective semiconductor devices are individually molded with molding compound and the respective molded semiconductor devices are stamped out to form individual semiconductor packages.
In the frame of the collectively molded type, as shown in FIG. 4(A), some molding cavities C of large size are provided within a frame F. Multiple semiconductor devices are arranged in a matrix within each molding cavity C, and are respectively and collectively molded with molding compound. Thereafter, the collectively molded semiconductor devices are cut at grid-leads L by means of a dicing saw so that a semiconductor package S shown in FIG. 4(B) is obtained. Namely, semiconductor devices are mounted on die-pads of lead frames through silver pastes and others and wire bonding is carried out. Thereafter, plural semiconductor devices are collectively molded with molding compound to a given cavity size, and then the collectively molded semiconductor devices are cut to form individual semiconductor packages by dicing.
In the above-mentioned semiconductor package of the collectively molded type, heat generated in the semiconductor device is transmitted through a die-pad to suspending leads, in which there is a case where suspending leads come off from the molded resin due to a difference in the thermal expansion coefficient between metal and resin. Therefore, in order to prevent the coming-off of the suspending leads, the suspending leads are formed with projection portions, or as shown in FIG. 2, the tips of suspending leads are formed into a forked shape, or a so-called fish tail shape.
Generally, in case of producing products by etching, parts designed to form a right angle are finished to have a roundish or rounded shape (R-shape), no matter how the etching process is carried out. In a frame for a semiconductor package of the collectively molded type having suspending leads formed into a fish tail shape, the R-shape formed by etching is also seen. For example, even if suspending leads 2 having a fish tail shape are designed as shown in FIG. 5, etched products have the R-shape as shown by the dotted line.
Semiconductors are mounted on the frame F for the semiconductor package of the collectively molded type, collectively molded, and thereafter divided into individual semiconductor packages by dicing. At this time, if the roundish part of the R-shape does not come to the dicing line α, there is no problem. However, if the roundish part of the R-shape comes to the dicing line α, because of the large R-shape, as shown in FIG. 6, a metal piece 8 of grid-lead L is left at an edge of the individual semiconductor package. Further, in a few cases, when mounting a semiconductor product on a substrate, the metal piece 8 comes off of the molded resin and drops down on the substrate, so that accidental short-circuiting is likely to occur.